Chapter 4 Statistics Review test

You want to know the opinions of American high school teachers on the issue of establishing a national proficiency test as a prerequisite for graduation from high school. You obtain a list of all high school teachers belonging to the National Education Association (the country's largest teachers' union) and mail a survey to a random sample of 2500 teachers. In all, 1347 of the teachers return the survey. Of those who responded, 32% say that they favor some kind of national proficiency test. Which of the following statements about this situation is true? (a) Since random sampling was used, we can feel confident that the percent of all American high school teachers who would say they favor a national proficiency test is close to 32%. (b) We cannot trust these results, because the survey was mailed. Only survey results from face-to-face interviews are considered valid. (c) Because over half of those who were mailed the survey actually responded, we can feel pretty confident that the actual percent of all American high school teachers who would say they favor a national proficiency test is close to 32%. (d) The results of this survey may be affected by nonresponse bias. (e) The results of this survey cannot be trusted due to voluntary response bias.

d) the results of this survey may be affected by non-response bias

You wonder if TV ads are more effective when they are longer or repeated more often or both. So you design an experiment. You prepare 30-second and 60-second ads for a camera. Your subjects all watch the same TV program, but you assign them at random to four groups. One group sees the 30-second ad once during the program; another sees it three times; the third group sees the 60-second ad once; and the last group sees the 60-second ad three times. You ask all subjects how likely they are to buy the camera. (a) This is a randomized block design, but not a matched pairs design. (b) This is a matched pairs design. (c) This is a completely randomized design with one explanatory variable (factor). (d) This is a completely randomized design with two explanatory variables (factors). (e) This is a completely randomized design with four explanatory variables (factors).

d) this is a completely randomized design with one explanatory variables (factors)

A study of treatments for angina (pain due to low blood supply to the heart) compared bypass surgery, angioplasty, and use of drugs. The study looked at the medical records of thousands of angina patients whose doctors had chosen one of these treatments. It found that the average survival time of patients given drugs was the highest. What do you conclude? (a) This study proves that drugs prolong life and should be the treatment of choice. (b) We can conclude that drugs prolong life because the study was a comparative experiment. (c) We can't conclude that drugs prolong life because the patients were volunteers. (d) We can't conclude that drugs prolong life because this was an observational study. (e) We can't conclude that drugs prolong life because no placebo was used.

d) we cant conclude that drugs prolong life because this was an observational study.

You want to take a simple random sample (SRS) of 50 of the 816 students who live in a dormitory on campus. You label the students 001 to 816 in alphabetical order. In the table of random digits, you read the entries 95592 94007 69769 33547 72450 16632 81194 14873 The first three students in your sample have labels (a) 955, 929, 400. (b) 400, 769, 769. (c) 559, 294, 007. (d) 929, 400, 769. (e) 400, 769, 335.

e) 400, 769, 335

An example of a non-sampling error that can reduce the accuracy of a sample survey is (a) using voluntary response to choose the sample. (b) using the telephone directory as the sampling frame. (c) interviewing people at shopping malls to obtain a sample. (d) variation due to chance in choosing a sample at random. (e) inability to contact many members of the sample.

e) inability to contact many members of the sample

In the experiment of the previous exercise, the 240 subjects are labeled 001 to 240. Software randomly assigns 60 subjects to each of the four diets. This is (a) a completely randomized design. (b) a randomized block design. (c) a matched pairs design. (d) an observational study. (e) an SRS.

a) a completely randomized design

Consider an experiment to investigate the effectiveness of different insecticides in controlling pests and their impact on the productivity of tomato plants. What is the best reason for randomly assigning treatment levels (spraying or not spraying) to the experimental units (farms)? (a) Random assignment makes the experiment easier to conduct since we can apply the insecticide in any pattern rather than in a systematic fashion. (b) Random assignment will tend to average out all other uncontrolled factors such as soil fertility so that they are not confounded with the treatment effects. (c) Random assignment makes the analysis easier since the data can be collected and entered into the computer in any order. (d) Random assignment is required by statistical consultants before they will help you analyze the experiment. (e) Random assignment implies that it is not necessary to be careful during the experiment, during data collection, and during data analysis.

b) Random assignment will tend to average out all other uncontrolled factors such as soil fertility so that they are not confounded with the treatments effects.

The Community Intervention Trial for Smoking Cessation asked whether a community-wide advertising campaign would reduce smoking. The researchers located 11 pairs of communities, each pair similar in location, size, economic status, and so on. One community in each pair participated in the advertising campaign and the other did not. This is (a) an observational study. (b) a matched pairs experiment. (c) a completely randomized experiment. (d) a randomized block design, but not matched pairs. (e) a stratified random sample.

b) a matched pairs experiment

Two essential features of all statistically designed experiments are (a) compare several treatments; use the double-blind method. (b) compare several treatments; use chance to assign subjects to treatments. (c) always have a placebo group; use the double-blind method. (d) use a block design; use chance to assign subjects to treatments. (e) use enough subjects; always have a control group.

b) compare several treatments, use chance to assign subjects to treatments.

The most important advantage of experiments over observational studies is that (a) experiments are usually easier to carry out. (b) experiments can give better evidence of causation. (c) confounding cannot happen in experiments. (d) an observational study cannot have a response variable. (e) observational studies cannot use random samples.

b) experiments can give better evidence of causation.

A researcher wishes to compare the effects of 2 fertilizers on the yield of soybeans. She has 20 plots of land available for the experiment, and she decides to use a matched pairs design with 10 pairs of plots. To carry out the random assignment for this design, the researcher should (a) use a table of random numbers to divide the 20 plots into 10 pairs and then, for each pair, flip a coin to assign the fertilizers to the 2 plots. (b) subjectively divide the 20 plots into 10 pairs (making the plots within a pair as similar as possible) and then, for each pair, flip a coin to assign the fertilizers to the 2 plots. (c) use a table of random numbers to divide the 20 plots into 10 pairs and then use the table of random numbers a second time to decide upon the fertilizer to be applied to each member of the pair. (d) flip a coin to divide the 20 plots into 10 pairs and then, for each pair, use a table of random numbers to assign the fertilizers to the 2 plots. (e) use a table of random numbers to assign the 2 fertilizers to the 20 plots and then use the table of random numbers a second time to place the plots into 10 pairs.

b) subjectively divide the 20 plots into 10 pairs (making the plots within a pair as similar as possible) and then, for each pair, flip a coin to assign the fertilizers to the 2 plots.

A simple random sample (SRS) is (a) any sample selected by using chance. (b) any sample that gives every individual the same chance to be selected. (c) a sample that gives every possible sample of the same size the same chance to be selected. (d) a sample that doesn't involve strata or clusters. (e) a sample that is guaranteed to be representative of the population.

c) a sample that gives every possible sample of the same size the same chance to be selected.

Corn variety 1 yielded 140 bushels per acre last year at a research farm. This year, corn variety 2, planted in the same location, yielded only 110 bushels per acre. Unfortunately, we don't know whether the difference is due to the superiority of variety 1 or to the effect of this year's drought. This is an example of (a) bias. (b) matched pairs design. (c) confounding. (d) the placebo effect. (e) replication.

c) confounding

A double-blind experiment was conducted to evaluate the effectiveness of the Salk polio vaccine. The purpose of keeping the diagnosing physicians unaware of the treatment status of the experimental subjects was to (a) eliminate grounds for malpractice suits. (b) ensure that subjects were randomly assigned to treatments. (c) eliminate a possible source of bias. (d) make sure nobody is harmed. (e) avoid the placebo effect.

c) eliminate a possible source of bias.

When we take a census, we attempt to collect data from (a) a stratified random sample. (b) every individual selected in an SRS. (c) every individual in the population. (d) a voluntary response sample. (e) a convenience sample.

c) every individual in the population

A simple random sample of 1200 adult Americans is selected, and each person is asked the following question: "In light of the huge national deficit, should the government at this time spend additional money to establish a national system of health insurance?" Only 39% of those responding answered "Yes." This survey.. (a) is reasonably accurate since it used a large simple random sample. (b) needs to be larger since only about 24 people were drawn from each state. (c) probably understates the percent of people who favor a system of national health insurance. (d) is very inaccurate but neither understates nor overstates the percent of people who favor a system of national health insurance. Since simple random sampling was used, it is unbiased. (e) probably overstates the percent of people who favor a system of national health insurance.

c) probably understates the percent of people who favor a system of national health insurance.

The Web portal AOL places opinion poll questions next to many of its news stories. Simply click your response to join the sample. One of the questions in January 2008 was "Do you plan to diet this year?" **More than 30,000 people responded, with 68% saying "Yes." You can conclude that (a) about 68% of Americans planned to diet in 2008. (b) the poll used a convenience sample, so the results tell us little about the population of all adults. (c) the poll uses voluntary response, so the results tell us little about the population of all adults. (d) the sample is too small to draw any conclusion. (e) None of these.

c) the poll uses voluntary response, so the results tell us little about the population of all adults.

Can changing diet reduce high blood pressure? Vegetarian diets and low-salt diets are both promising. Men with high blood pressure are assigned at random to four diets: (1) normal diet with unrestricted salt; (2) vegetarian with unrestricted salt; (3) normal with restricted salt; and (4) vegetarian with restricted salt. This experiment has (a) one factor, the type of diet. (b) two factors, high blood pressure and type of diet. (c) two factors, normal/vegetarian diet and unrestricted/restricted salt. (d) three factors, men, high blood pressure, and type of diet. (e) four factors, the four diets being compared.

c) two factors, high blood pressure and type of diet

Your statistics class has 30 students. You want to call an SRS of 5 students from your class to ask where they use a computer for the online exercises. You label the students 01, 02,..., 30. You enter the table of random digits at this line: 14459 26056 31424 80371 65103 62253 22490 61181 Your SRS contains the students labeled (a) 14, 45, 92, 60, 56. (b) 14, 31, 03, 10, 22. (c) 14, 03, 10, 22, 22. (d) 14, 03, 10, 22, 06. (e) 14, 03, 10, 22, 11.

d) 14, 03, 10, 22, 06

A report in a medical journal notes that the risk of developing Alzheimer's disease among subjects who (voluntarily) regularly took the anti-inflammatory drug ibuprofen (the active ingredient in Advil) was about half the risk among those who did not. Is this good evidence that ibuprofen is effective in preventing Alzheimer's disease? (a) Yes, because the study was a randomized, comparative experiment. (b) No, because the effect of ibuprofen is confounded with the placebo effect. (c) Yes, because the results were published in a reputable professional journal. (d) No, because this is an observational study. An experiment would be needed to confirm (or not confirm) the observed effect. (e) Yes, because a 50% reduction can't happen just by chance.

d) No, because this is an observational study. An experiment would be needed to confirm (or not confirm) the observed effect.

Archaeologists plan to examine a sample of 2-meter-square plots near an ancient Greek city for artifacts visible in the ground. They choose separate random samples of plots from floodplain, coast, foothills, and high hills. What kind of sample is this? (a) A cluster sample (b) A convenience sample (c) A simple random sample (d) A stratified random sample (e) A voluntary response sample

d) a stratified random sample

A TV station wishes to obtain information on the TV viewing habits in its market area. The market area contains one city of population 170,000, another city of 70,000, and four towns of about 5000 inhabitants each. The station suspects that the viewing habits may be different in larger and smaller cities and in the rural areas. Which of the following sampling designs would give the type of information that the station requires? (a) A cluster sample using the cities and towns as clusters (b) A convenience sample from the market area (c) A simple random sample from the whole market area (d) A stratified sample from the cities and towns in the market area (e) An online poll that invites all people from the cities and towns in the market area to participate

d) a stratified sample from the cities and towns in the market area

Bias in a sampling method is (a) any error in the sample result, that is, any deviation of the sample result from the truth about the population. (b) the random error due to using chance to select a sample. (c) any error due to practical difficulties such as contacting the subjects selected. (d) any systematic error that tends to occur in the same direction whenever you use this sampling method. (e) racism or sexism on the part of those who take the sample.

d) any systematic error that tends to occur in the same direction whenever you use this sampling method.

The drug manufacturer Merck recently stopped testing a promising new drug to treat depression. It turned out that in a randomized, double-blind trial, a dummy pill did almost as well as the new drug. The fact that many people respond to a dummy treatment is called (a) confounding. (b) nonresponse. (c) comparison. (d) the placebo effect. (e) bias.

d) the placebo effect